On Ralvery someone posted a link to this YouTube video on using a gathering foot http://www.youtube.com/watch?v=3AZiyQs44kU
So I tried it on some material I had.
For this foot, you need to remove the foot holder because this is a long shank type foot. I didn't change the thread length and could have. I started with auto Tension, which didn't gather at all, then went to +2, gathered a bit; up to +2.5, gathered more; up to+3 and pretty much ruffled.
I left the speed on middle ground and used my foot peddle--as usual.
I found after that I could pull the fabric to create a gather near the auto tension part.
The instruction manual does say you can use two pieces of fabric, one to gather and one not gathered, but I think I would prefer to use one for more control.